If Nick Clegg debates well tonight, put the following dates in your diary: 11 May, 13 May and 20 May. Things could get interesting.

These are the dates of the next three government debt auctions after the election. And, judging from recent activity, the UK Debt Management Office will want to borrow around £7bn from investors in this post-election fortnight of potentially huge political turmoil. It might sound like unfortunate timing, but this is a normal level of activity – well, normal for a year when the public sector borrowing requirement is £163bn.

So far, it has been a relatively painless process. The DMO auctions are regularly oversubscribed and Britain has not been forced to pay the sort of interest rate premium suffered by countries like Greece. All other things being equal, I strongly suspect we will continue to manage OK and things will get easier as the economy improves and the deficit comes down. But it pays to consider the worst-case scenario for a moment.

As plenty of my political colleagues have pointed out, the perversities of our electoral system could throw up a major consitutitional crisis if the Lib Dems continue to do well. The newly-crowned "party of change" could easily end up with the largest share of the vote and remain a distant third in numbers of seats, with a devastated Labour party somehow still in front. Will Gordon Brown try to cling to office? Will Peter Mandelson engineer a coup to put David Milliband, Nick Clegg, or even himself in place? And most importantly, will the country, Queen and civil service stand for such a perverse anti-democratic outcome?

Hopefully, such questions would get resolved in a matter of weeks, not months, but it is far from guaranteed that it will all get wrapped up in a weekend. In the meantime, investors will be making up their minds whether to buy billions of pounds of our national debt. Sterling would probably start to slide and the cost of borrowing would climb sharply if there was any sign that they were staying away because they did not know who was in charge.

Crucially, this is not an argument against coalition governments either. Finer financial minds than mine have powerfully argued that consensus politics might actually be just what we need to tackle the economic challenges ahead. Once things settle down into a stable coalition, we will be fine. The question is how long will that take if the electoral math is really perverse?

Talking to one of the biggest British buyers of gilts this morning, I was struck by three things:

• The markets don't fear a change of government or a coalition; they fear uncertainty. In private, most business leaders acknowledge that all the three parties will probably do much the same thing about the deficit – as long as they are left to get on with it unchecked by electoral pressures.

• The markets move fast. In the current febrile climate, a constitutional crisis would be matched by daily, or even hourly, movements in sterling and gilts."They would have until the Monday to sort it out or things will start to wobble," said my source (one of the top dozen or so names in the City).

• In the long run, it only matters if it drags on. The negative feedback loop only becomes really scary if the gilts panic pushes up interest rates to the point where it chokes off the recovery. That would probably take months.

This last point is worth hanging on to next time the Lib Dem bashers start scaremongering. One hopes that even Gordon Brown would be persuaded to leave quietly if things were getting this bad, and pretty soon, it would blow over. But it's a powerful reason to think about better constitutional arrangements for next time around.